The present invention relates to a method and apparatus for erasing information from optical recording tape with a thermo-deforming layer, and particularly to a method and apparatus for optically erasing information using an optical system which scans a tape with focused light.
Referring to Japanese laid-open patent publication No. 1-294238 and U.S. Pat. No. 4,398,203, an information medium is introduced in which information is optically recorded and read. Different from conventional magnetic, optical, or magneto-optical media, the information medium has a thermo-deforming layer which is viscoelastically thermo-deformed, and records information according to the arrangement of bumps created by heating portions of the thermo-deforming layer.
The basic structure and record/playback principle of the medium are illustrated in FIGS. 1A, 1B and 1C. Referring to FIG. 1A, the medium comprises a supporting layer 1, a thermo-deforming layer 2, and protective layer 3 which are stacked in order. When laser light 5 is projected on thermo-deforming layer 2, the portion which is irradiated by laser light 5 is heated by its thermal energy and expands viscoelastically as shown in FIG. 1B. Then, when cooled, the expanded portion contracts by viscoelastical deformation to render a bump 4 having a different residual stress than the original planar form as shown in FIG. 1C. Thus, it is possible to optically record information by discontinuously forming the bumps while projecting modulated laser light. In addition, when laser light is induced to the degree where the thermo-deforming layer does not yet expand from the heat, optical reproduction of the information can be done by detecting light modulated and reflected by the bumps. Further, since the thermo-deforming layer becomes planar by being heated to remove the residual stress of the bumps, erasing the information is also possible by means of a heater capable of evenly heating the entire thermo-deforming layer.
Optical recording media with such a thermo-deforming layer may be manufactured, for example, in cassette tape form, and a broad application of uses for such a thermo-deforming layer could include computer memory devices, processing of information, audio players and video players.
In FIG. 2, tape T, an optical recording medium is wound on two reels R and R' in a cassette C. A heater EH is used as an erase head and an optical means OH is used as a record/playback head. The two heads are provided in close proximity to tape T which travels between the two reels R and R', and passes near the heater EH which is in the form of a plate or a rod and installed without making direct contact with tape T. In other words, the conventional erasing method uses radiant heat from the heater EH which heats tape T as it passes, the tape then cools as it proceeds past the influence of heater EH.
Erasing by heat, however, is disadvantageous in that first, since the environment influences the heater, maintaining a proper and uniform heating temperature is difficult; second, the erasing operation is delayed because the heater requires time to rise to a predetermined temperature; and finally, while cooling, an additional heat shielding means or a cooler is required in order to interrupt the influence of radiant heat from the heater EH.